The present invention relates to a new and improved mold for, and method of, fabricating a perforated body for receiving textile fibers or fibrous material deposited on a fiber receiving surface of the perforated body by means of an airstream and for passage of the airstream through perforations of the perforated body. The perforated body is advantageously used as a friction spinning means or element which, in turn, is used in a friction spinning device.
The present invention also relates to a new and improved construction of a composite friction spinning element for use with a friction spinning device.
The purpose of the friction spinning device is to take up fibers fed to a fiber receiving surface of the friction spinning means which may assume the shape of, for example, a perforated drum or disc or belt, in known manner by means of an air stream and to twist the fibers into a yarn or the like in a yarn formation region of a convergent zone formed by, for example, two cooperating friction spinning drums or a friction spinning disc and its cooperating conical roller. The yarn is withdrawn in a direction extending substantially at right angles to the direction of rotation of the friction spinning drums.
An example of the previously mentioned friction spinning method or process and a spinning device in which a friction spinning drum is used, has been disclosed in the commonly assigned European Published Patent Application No. 175,862. From that published patent application it is also apparent that the friction spinning means or element does not have to be in the form of a perforated drum; it could also, for instance, comprise a perforated disc combined with a conical roller.
Two perforated drums, as disclosed in the German Patent No. 2,449,583, or one imperforate drum and one perforated drum, or an imperforate conical roller and a perforated disc, as disclosed in the aforementioned European Published Patent Application No. 175,862, can be used as friction spinning means or elements.
The airstream required for transporting the fibers is drawn by suction through the holes or perforations in the friction spinning drum, friction spinning disc or friction spinning belt by means of an appropriately located suction nozzle, for example, in the interior of the friction spinning drum or below the friction spinning disc. It is therefore clear that the holes or perforations of this friction spinning means or element must have a cross-section or cross-sectional area in the narrowest section or region of each of the holes or perforations which, on the one hand, is so small that it substantially prevents take-up of too many fibers by these holes or perforations during deposition on the fiber receiving surface of the friction spinning means; such fibers may be either sucked away and lost, or at least cut on an edge of the mouth of the suction nozzle and thereby shortened.
On the other hand, the energy consumption of equipment of this kind should be held as low as possible, the required quantity and flow rate of air making up a substantial part of the energy consumption. Furthermore, efforts should be made to oppose the tendency towards blockage of the holes or perforations. In friction spinning means of this kind, it is therefore desirable to select the hole or perforation section at the narrowest region or throat to be as large as possible from this viewpoint.
However, these requirements placed on the hole or perforation diameter stand in direct opposition to each other.
From practical operation and from patent publications, for example, German Published Patent Application No. 3,114,093, it is known that these holes or perforations, when formed with a circular cross-section or cross-sectional configuration, generally have a diameter between 0.5 and 0.8 mm.
However, the perforated drums must have inherent stiffness or rigidity so that no deformation arises in use. This calls for a minimum wall thickness of at least 1 mm when brass is used with, for example, a drum diameter of 50 mm.
It is, however, apparent that boring of such small holes or perforations, where the number of holes or perforations is in the region of several tens of thousands of holes or perforations per drum, in a material of 1.0 to 1.5 mm or greater thickness, cannot be carried out without problems and is therefore expensive.
If additional demands are placed upon the form or configuration of the holes or perforations, as in the case of German Published Patent No. 2,919,316, then the manufacturer of such perforated drums is faced with special problems.
In the art of manufacturing spinnerets, it is known, for example, from U.S. Pat. No. 3,167,489 to produce a perforated plate by electroforming or galvanic deposition on a support plate from which filaments are extended under tension. The filaments are removed after the electroforming process and thus define the holes or perforations in the galvanically deposited plate. In a further known process such as known from U.S. Pat. No. 3,332,858, there is formed a mold containing protrusions which correspond to the desired spinneret holes or perforations. After the electroforming operation or galvanic deposition and removal from the mold, the protuberances formed at the location of the mold protrusions, are machined away to produce the spinneret.
In the art of galvanoplastic sieve or grid manufacture, it is known to produce a sieve or grid containing widening holes or perforations by electroforming or galvanic deposition of the sieve or grid material on a metallic support plate containing a non-conductive sieve or grid image which is sunk into or placed upon the surface at which the sieve or grid is formed, see the publication by H. J. Heinrich, entitled "Galvanoplastic Sieve Manufacture" in the Journal "Metalloberflache", Vol. 19, No. 12, pages 369 to 372, 1965.